1. Field of the Invention
The invention relates to a hierarchical network management system comprising:
1a) concentrators between the separate levels of the hierarchy and PA1 1b) interfaces in the concentrators for point-to-point and bus connections. PA1 1c) an interface for a bus connection on the master side, which takes delays into consideration and to which a transmission channel can be connected, which channel comprises a forward and a return line and to whose line apparatus addressable in parallel are connected, PA1 1d) a controllable change-over switch inserted in the return line of the transmission channel and provided for each addressable apparatus of the parallel combination.
2. Description of the Related Art
A management system having these characteristic features is provided, for example, in the CCITT Recommendation M.30 (cf. the Blue Book), which will be referenced as (D1) in the following. Concretizations of such management systems are described, for example, in DE 34 36 44 1 A1 and in a data paper of Philips Kommunikations Industrie AG (SISA Kommunikationsnetz fur Netzmanagement, March 1991). These two documents will be referenced (D2) and (D3) in the following.
Specifically for the management system according to (D3) it holds that the network elements to be monitored are to comprise a serial interface via which the messages from the network elements within the system are transmitted to network monitoring positions. Since all the lines of the system are bidirectional, control instructions and also user data can be transmitted to the network elements to be monitored. The network observation desk at which the messages of all the network elements to be monitored come together, is to be called a central observation desk here.
The user of an information transmission network has, aided by such a management system, the possibility of continuously providing himself with an idea of the state of his transmission network by evaluating the protocols arriving at the central observation desk. This idea includes, for example, differentiated reports on malfunctionings of the transmission network as well as on the quality of the transmission. On the basis of this information the network user may then timely and purposefully take measures, for example, utilize a substitute circuit, so that always optimum use is made of the capacity of his transmission network.
The communication of the management system according to (D3) is based on the so-called master-slave principle. Up to thirty concentrators or network elements can be connected as slaves to a master concentrator. The master interrogates his slaves for telegrams with the aid of addresses and transfers these telegrams to the concentrator or the network observation desk by which he is interrogated himself by means of an address.
In this manner there is a hierarchical structure which is subdivided into so-called addressing levels. This hierarchical structure is called tree structure in (D2). On an addressing level--called level for short--there is a concentrator as master which interrogates at least two connected apparatus by way of addresses. An apparatus is here to be understood as either a network element or a concentrator. A network element is a component of the transmission network to be monitored.
A disadvantage in the SISA system described in (D3) is the fact that the number of levels is limited to ten. As a result, a maximum of five network elements of the line structure such as, for example, the intermediate regenerators of a transmission section, can be monitored by the system. Connecting intermediate regenerators via a bus interface having the electrical properties as stated in V.11 (cf.(D3)) to a concentrator is impossible.
Point-to-point connections by which larger distances can be bridged, however, are only provided for interconnecting the concentrators. For this purpose, two concentrators should be installed at each intermediate regenerator. One concentrator connected via a point-to-point connection to the concentrator of the next higher level and which furthermore comprises a bus connection to which a second concentrator and the intermediate regenerator are connected. The second concentrator is connected via a point-to-point connection to the first concentrator of the next intermediate regenerator. The number of permitted levels would then be reached with the fifth intermediate regenerator at the latest.